Conventional headlight lamps, whether of the sealed beam variety or not, typically utilize a paraboloid reflector with an incandescent filament lamp located at, and centered on, the focal point of the reflector. Recently, the typical incandescent filament lamp used in such headlights includes a tungsten halogen capsule or bulb in which a tungsten filament is contained in a gaseous halogen atmosphere enclosed by a cylindrical glass or quartz envelope.
The function of the paraboloid reflector is to reflect the light emitted from the lamp filament and direct the light rays forward in a collimated beam of substantially parallel rays. Typically, a lenticular lens is disposed forward of the reflector and lamp filament in the path of the parallel light rays. The lens includes an array of lenticules, or lens elements, which isolate pencils of the collimated light beam. These lens elements modifiy such pencils of light in direction and/or distribution to provide the predetermined desired headlamp light distribution pattern.
The most significant portions of the headlamp light distribution pattern are develdoped using the prism power of the lens elements. If the prism power required to deviate the beam is too large, undesirable light dispersion and consequential color banding occurs. Even at lower prism powers, added problems can arise. Offsets, or steps, are typically required between lens elements. The size of these steps increases with prism angle and therefore with prism power. These steps introduce stray light into the beam as a result of surface reflection as well as the prism power of the steps. Large offsets, or steps, are also disadvantageous from the standpoint of glass or plastic fabrication. It is relatively difficult to maintain the quality of molded parts as the depth of offsets becomes appreciable with respect to the total part thickness.
Accordingly, a need exists for a reflector/filament combination which, when used with a lenticular lens array, minimizes the amount of lens element prism power required to obtain the desired headlamp light distribution pattern.